Microwave switches are often used in satellite communication systems where reliability of system components is important. Accordingly, microwave switches are commonly used in Switch Routing Matrices or in Redundancy Rings. The Switch Routing Matrices allow for a number of inputs to be connected to a number of outputs of the matrix. There are two groups of Switch Routing Matrices: one group being the non-blocking and non-interrupting such as crossbar or crosspoint switch matrices; the other group being just non-blocking switch routing matrices, such as rearrangeable switch matrices, diamond switch matrices, rectangular switch matrices, rhomboidal switch matrices, pruned rectangular switch matrices, Bose-Nelson switch matrices, etc. The Redundancy Rings are switch arrays that have usually one or two columns of T-switches (for input) and reroute a number of channels to spare Traveling Wave Tube Amplifiers (TWTA) in case of TWTA failure. The preference there is to use the T-switches to create the redundancy rings with the minimum number switches that are capable to match the output redundancy rings.
In the current switch matrix architectures there are always cross over points between signal paths either between switches or internal to a microwave switch since the signal paths are on the same plane in both cases. The cross over points of signal paths result in design and performance problems both for coaxial and planar technology.
In general, the RF electromechanical switches currently used to implement RF switch matrices are usually bulky and increase the mass of the switch matrix. Furthermore, the use of cables to achieve all required connections results in increased mass and volume of the assembly and increase RF losses for the matrix. This can be significant since switch matrices are used in spacecraft applications where low mass is important.
However, there is currently a movement towards the development of RF MEMS (Micro Electro-Mechanical Systems) switches. These are a new class of planar devices distinguished by their extremely small dimensions and the fabrication technology, which is similar to integrated circuits and allows for batch machining. An RF MEMS switch is constructed on a substrate of an integrated circuit and has a micro-structure with an active element that moves in response to a control voltage, or other control techniques as is commonly known to those skilled in the art, to provide the switching function.
RF MEMS switches have a number of advantages over RF electro-mechanical switches. For instance, since RF MEMS switches are batch machined, their cost represents only a small fraction of the cost of an equivalent conventional bulky electro-mechanical RF switch. Also, the cost does not increase significantly with the number of switches manufactured. Furthermore, since a typical spacecraft employs several hundred microwave switches, the light weight of an RF MEMS switch will provide a reduction in weight which can result in significant cost savings. However, currently there are no commercially available RF MEMS switch matrices.